The present invention relates generally to microplates for assaying samples, and more specifically to microplates that have UV permeable bottom wells and methods of making such microplates.
The recent growth in many areas of biotechnology has increased the demand to perform a variety of studies, commonly referred to as assays, of biochemical systems. These assays include, for example, biochemical reaction kinetics, DNA melting point determinations, DNA spectral shifts, DNA and protein concentration measurements, excitation/emission of fluorescent probes, enzyme activities, enzyme-cofactor assays, homogeneous assays, drug metabolite assays, drug concentration assays, dispensing confirmation, volume confirmation, solvent concentration confirmation and solvation confirmation. Since most components of biochemical systems absorb radiation in the ultraviolet (UV) region of the electromagnetic spectrum (200 nm to 400 nm), UV absorption spectroscopy may be used to study these systems. In addition, UV absorption spectroscopy offers the advantages of relatively high precision and accuracy.
Assays of biochemical systems are carried out on a large scale in both industry and academia, so it is desirable to have an apparatus that allows these assays to be performed in a convenient and inexpensive fashion. Because they are relatively easy to handle and low in cost, microplates are often used for such studies. Microplates typically consist of a plurality of individual wells formed of polymeric materials. Each well includes sidewalls and a bottom so that an aliquot of a sample may be placed within each well. The wells may be arranged in relatively close proximity in a matrix pattern, allowing samples to be studied individually or as a group. Common sizes for microplates include matrices having dimensions of 4xc3x976 (24 wells) or 8xc3x9712 (96 wells), although larger microplates are also used that may include matrices of hundreds or even thousands of wells.
Typically, the materials used to construct a microplate are selected based on the samples to be assayed and the analytical techniques to be used. For example, the materials of which the microplate is made should be chemically inert to the components of the sample, and the materials should be impervious to radiation or heating conditions to which the microplate is exposed during the course of an experiment. Thus, a microplate used in assaying samples by UV absorption should have a UV permeable bottom sheet so that a substantial amount UV radiation can pass through each well and interact with the sample without being absorbed by the well bottom.
Despite the potential advantages of employing microplates having UV permeable bottom sheets, there has been limited progress in manufacturing such microplates. One problem in designing these microplates relates to the polymeric materials that are typically used for microplate construction. In particular, these polymeric materials usually have relatively high UV absorption probabilities. Absorption of UV radiation by the polymeric materials results in the chemical and physical degradation of the microplates. Therefore, to prolong the lifetime of these microplates, UV stabilizers specifically designed to absorb UV radiation are often added to the polymeric materials. As a result, most known microplates have exceptionally high UV absorption probabilities, rendering them useless for experiments in which UV absorption of samples is used.
U.S. Pat. No. 5,487,872 to Hafeman et al. (Hafeman) discloses a microplate designed for assaying samples with UV absorption techniques. Hafeman discloses a variety of materials from which the bottom surface of the microplate wells may be formed, including TPX(copyright) 4-methylpentene-1 polymer as the preferred material (Mitsui Petrochemical Industries, Japan). However, it is believed that microplates using this material for the well bottoms may have limited sensitivity in certain biochemcial experiments. For example, in nucleic acid studies, UV absorption in a range between approximately 260 nm to approximately 280 nm is studied, but TPX(copyright) has a relatively high optical density in this wavelength range.
Microplates having a quartz bottom plate glued to a molded body have also been produced. However, the cost of these microplates is often more than two orders of magnitude higher than the cost of a microplate formed entirely from polymeric materials, precluding their use for most studies. In addition, the materials used to bond the quartz bottom plate to the microplate body may leach into samples contained within the wells of the microplate, contaminating the samples and compromising the reliability of the experimental results. Furthermore, over time, the strength of the bond between the bottom plate and the body may deteriorate and form leaks between sample wells.
Hence, it remains a challenge in the art to provide a microplate that is relatively inexpensive, comparatively durable and includes well bottoms having an acceptable optical density across the entire useful range of the UV spectrum.
In one illustrative embodiment of the invention, a microplate is provided that comprises a frame that forms sidewalls of at least one well and a first layer that forms a bottom of the at least one well. The first layer is formed from a plastic material having an average optical density no more than approximately 0.09 at a thickness of approximately 7.5 mils between wavelengths of approximately 200 nm and approximately 300 nm.
In another illustrative embodiment of the invention, a microplate is provided that comprises a frame and a sheet. The frame includes an upper portion and a lower portion that is contiguous with the upper portion. The upper portion of the frame defines sidewalls of at least one well. The sheet defines a bottom of the at least one well, and at least a portion of the sheet is disposed between the upper and lower portions of the frame.
In yet another illustrative embodiment of the invention, a method is provided for making a microplate having at least first and second wells, each of the first and second wells having sidewalls and a bottom. The method comprises steps of: (A) inserting a sheet of a first material into a mold cavity that includes sections shaped to form the sidewalls of the first and second wells so that the sheet is positioned to form the bottoms of the first and second wells, the first material having an average optical density that is no more than approximately 0.09 at a thickness of approximately 7.5 mils between wavelengths of approximately 200 nm and approximately 300 nm; (B) injecting a molten plastic material into the mold cavity; and (C) cooling the plastic material to form the microplate with the plastic material forming the sidewalls of the first and second wells and the sheet of the first material forming the bottom of each of the first and second wells.
In a further embodiment of the invention, a method is provided for forming a microplate. The method comprises steps of: (A) providing an upper plate defining sidewalls of at least one well, the upper plate having a lower surface; (B) adhering an intermediate layer to the lower surface of the upper plate; and (C) adhering a sheet of the first material to the intermediate layer so that the sheet of the first material forms a bottom of the at least one well.
In yet a further embodiment of the present invention, a method is provided for making a microplate having at least first and second wells, each of the first and second wells having sidewalls and a bottom. The method comprises steps of: (A) inserting a sheet of a material having at least one hole into a mold cavity that includes sections shaped to form the sidewalls of the first and second wells so that the sheet is positioned to form the bottoms of the first and second wells; (B) injecting a molten first plastic material into the mold cavity; and (C) cooling the first plastic material to form the microplate with the first plastic material forming the sidewalls of the first and second wells and the sheet of the first material forming the bottom of each of the first and second wells.
In still a further illustrative embodiment of the invention, a microplate is provided that comprises a frame that forms sidewalls of at least one well and a first layer that forms a bottom of the at least one well. The first layer is formed from a chlorotrifluoropolyethylene, such as Aclar(copyright) film, and may have an average optical density of no more than approximately 0.09 at a thickness of approximately 7.5 mils, or may have a larger value if copolymer(s) are incorporated therein.